The high-affinity sulfonylurea receptor (SUR1) expressed on the beta cells of the pancreas is a key component in glucose-stimulated insulin secretion. The investigators have previously reported linkage of 2-hour plasma glucose levels to a region near the SUR1 gene in Mexican Americans and observed a silent variant in exon 31 of the gene which was associated with high insulin concentrations in non-diabetic members of Mexican American type 2 diabetic families. It is not known whether this is due to primary oversecretion of insulin or compensatory insulin response to insulin resistance. This study will compare insulin secretion and insulin resistance in 15 non-diabetic Mexican Americans homozygous for this variant of the SUR1 gene and 15 subjects who are homozygous for the wildtype allele and who were previously genotyped participants of the San Antonio Family Diabetes Study.